Display device and method of manufacturing the same

ABSTRACT

Disclosed herein is a display device, including a display element, a first scanning line, a second scanning line, a data signal line, a switching element having a first terminal and a second terminal of a first conduction type, the first terminal being connected to the data signal line, for being held in a conducting state or a non-conducting state according to a voltage applied to the first scanning line, and a storage capacitance having a first electrode and a second electrode that shares the second scanning line, wherein the second terminal of the switching element is connected to the display element and connected to the first electrode of the storage capacitance including a semiconductor film of a second conduction type different from the second terminal.

The subject matter of application Ser. No. 10/442,374 is incorporatedherein by reference. The present application is a continuation of U.S.application Ser. No. 10/442,374, filed May, 21, 2003, now U.S. Pat. No.6,888,164, which claims priority to Japanese Patent Application NoJP2002-151322, filed May 24, 2002. The present application claimspriority to these previously filed applications.

BACKGROUND OF THE INVENTION

The present invention relates to a display device and a method ofmanufacturing the same, and particularly to a liquid crystal displaydevice and a method of manufacturing the same.

With characteristics of being thin and low power consumption, liquidcrystal display devices are widely used in notebook computers, displaydevices for car navigation, personal digital assistants (PDAs), portabletelephones and the like. The liquid crystal display device is roughlyclassified into a transmissive type that controls light from a backlightfor display, a reflective type that reflects extraneous light such assunlight or the like for display, or a recent display device referred toas a transflective type that combines characteristics of both thetransmissive type and the reflective type.

Applications of these display devices require that the display devicesconsume low power, and therefore a high aperture ratio is required tomaximize efficiency of use of the backlight. In the transflective type,a transmission part and a reflection part are formed in the same pixel,and thus multiple functions are incorporated within the pixel; it istherefore necessary to use space as effectively as possible.

In displaying an image on a liquid crystal display device, a scanningpulse is applied from a scanning line to a switching element, forexample a TFT (Thin Film Transistor) provided for each pixel, and theswitching element is turned on/off, whereby display pixels are selected.A signal corresponding to a video signal is applied to a data line, andthen applied via a source and a drain of the TFT to electrodes that havea liquid crystal sandwiched therebetween, whereby light entering theliquid crystal is modulated to display the image.

Within a period until a next writing operation after a voltagecorresponding to the video signal is written to each pixel, chargeresulting from the voltage applied to the electrodes of the liquidcrystal leaks through the liquid crystal and the switching element andis thus changed. In order to insure display picture quality, the appliedvoltage needs to be retained. Accordingly, an auxiliary capacitance (CS)sufficient as compared with the amount of leakage is generally formed inthe liquid crystal display device.

FIG. 1 is an example of an equivalent circuit diagram of a conventionalliquid crystal display device. FIG. 2 is a plan view of a configurationof the liquid crystal display device shown in FIG. 1.

FIG. 1 shows an equivalent circuit of 2×3 pixels. One pixel in theequivalent circuit includes a liquid crystal element and electrodeshaving the liquid crystal element sandwiched therebetween, a transistorTr as a switching element, and an auxiliary capacitance CS. Ccl1 to Ccl6denotes a capacitance of a liquid crystal capacitor formed by a liquidcrystal element and a display electrode and a common electrode havingthe liquid crystal element sandwiched therebetween. CS1 to CS6 denotes acapacitance value of the auxiliary capacitance of each pixel.

A plurality of scanning lines WLn−1, WLn, and WLn+1 are arranged inparallel with each other, and each connected to gate electrodes oftransistors Tr1 and Tr4, transistors Tr2 and Tr5, or transistors Tr3 andTr6 formed by TFTs, for example. The scanning lines WLn−1, WLn, andWLn+1 effect ON/OFF control of each of the transistors and therebyselect pixels.

Data signal lines BLn−1, BLn, and BLn+1 arranged in parallel with eachother apply a voltage corresponding to a video signal to each pixel. Thedata signal lines BLn−1, BLn, and BLn+1 are connected to for example asource region of the transistors Tr1, Tr2, and Tr3 or the transistorsTr4, Tr5, and Tr6. The data signal lines BLn−1, BLn, and BLn+1 applyvoltage to electrodes on both sides of liquid crystal elements in pixelsselected by the scanning line WLn−1, WLn, or WLn+1 while chargingauxiliary capacitances CS in the pixels, whereby light entering theliquid crystal elements is modulated to display an image.

FIG. 2 is a view of the configuration of scanning lines, data signallines, and one pixel formed on a transparent substrate. As shown in FIG.2, the auxiliary capacitance CS1 is formed on an auxiliary capacitanceline CSLn−1 as one electrode of the auxiliary capacitance CS1. Oneimpurity region, for example the source region of the transistor Tr1 isconnected to the data signal line BLn−1 via a conductive materialdeposited in a contact hole H1. Another impurity region, for example adrain region of the transistor Tr1 is connected to another electrodeformed by a semiconductor, for example, of the auxiliary capacitance CS1and an ITO electrode of an upper layer not shown in the figure viaconductive material deposited in contact holes H2 and H3.

An N-channel type thin film transistor TFT is generally used as thetransistors Tr1, . . . , Tr6. Specifically, N-type source and drainimpurity regions are formed by injecting phosphorus (P) or the like intosemiconductor thin film on both sides of a gate electrode. When apositive voltage equal to or higher than a threshold value is applied tothe gate electrode (scanning line), an N-channel formed by an N-typeinversion layer is formed between the source and the drain, whereby thesource and the drain are electrically connected to each other. That is,the transistor is in an ON state. When a voltage lower than thethreshold value is applied to the gate electrode (scanning line), on theother hand, the channel for electrically connecting the source and thedrain to each other is not formed, and therefore the transistor is in anOFF state.

The auxiliary capacitance CS1 is generally formed by a MOS structure ofa semiconductor layer, an insulating film, and a metal, which structurecan form a highest capacitance. In FIG. 2, the auxiliary capacitance CS1is for example formed by the auxiliary capacitance line CSLn−1 (metal),a gate insulating film forming the transistor Tr1, and theabove-mentioned N-type semiconductor film having phosphorus or the likeinjected therein. Such a MOS capacitance will hereinafter be referred toas an N-type MOS structure.

When the electrodes of the auxiliary capacitance are to be set at afixed potential, the auxiliary capacitance portion is generally made tobe of the N-type MOS structure.

In a case of common-inversion driving in which auxiliary capacitanceelectrodes are oscillated in phase with a counter electrode, thesemiconductor film forming the auxiliary capacitance CS does not form asufficient capacitance in an intrinsic state. Therefore, thesemiconductor layer is generally metalized, that is, made to contain ahigh concentration of phosphorus (made to be of an N+ type) or boron(made to be of a P+ type).

With the above conventional method, high-concentration injection ofphosphorus (allowing the semiconductor layer to be of the N+ type) orboron (allowing the semiconductor layer to be of the P+ type) isrequired to be performed only once, and therefore manufacturing cost canbe reduced.

However, the above structure requires an independent auxiliarycapacitance line, thus presenting a problem of a decrease in an apertureratio.

Accordingly, a CS-on-gate structure is proposed in which a scanning line(gate line) in a preceding stage or a succeeding stage also serves asthe auxiliary capacitance line.

FIGS. 3A and 3B show another example of a conventional liquid crystaldisplay device. FIG. 3A is an equivalent circuit diagram of the liquidcrystal display device, and FIG. 3B is a plan view of a configuration ofthe liquid crystal display device. In FIGS. 3A and 3B, the samecomponents as in FIG. 1 are designated by using the same referencenumerals, and their repeated description will be omitted whereappropriate.

FIG. 3A shows an equivalent circuit of 2×2 pixels. In FIG. 3A, auxiliarycapacitances CS1, CS4, CS2, and CS5 are directly connected to scanninglines WLn−1, WLn, and WLn+1 in place of the auxiliary capacitance linesCSLn−1, CSLn, and CSLn+1 shown in FIG. 1.

FIG. 3B shows a configuration of scanning lines, data signal lines, andone pixel formed on a transparent substrate. The auxiliary capacitanceCS1 is formed so as to overlap the scanning line WLn in place of theauxiliary capacitance line CSLn−1 shown in FIG. 2.

Also in this case, an N-channel type thin film transistor TFT isgenerally used as transistors Tr1, . . . , Tr6. Also, the auxiliarycapacitance CS1 is an N-type MOS capacitance. Specifically, when apositive voltage equal to or higher than a threshold value is applied togate electrodes (scanning lines) of the transistors Tr1, . . . , Tr6,the transistors Tr1, . . . , Tr6 are brought into an ON state. When avoltage lower than the threshold value is applied to the gateelectrodes, the transistors Tr1, Tr6 are brought into an OFF state.

As shown in FIG. 3B, the auxiliary capacitance CS1 is formed by thescanning line WLn (metal), a gate insulating film forming the transistorTr1, and an N-type semiconductor film having phosphorus or the likeinjected therein.

Such a CS-on-gate structure eliminates the need for forming theindependent auxiliary capacitance line, and therefore has an advantageof increasing the aperture ratio.

In order to maintain the NMOS transistor Tr1 in an off state, thepotential of the scanning lines WLn−1, WLn, . . . may generally be setto about 0 V to −6 V. In addition, the transistor Tr1 in the liquidcrystal display device is maintained in the OFF state during most of aperiod of display of one screen. That is, the potential of the scanninglines is maintained at 0 V or lower during most of the display period.

However, in the case of the CS-on-gate structure as shown in FIGS. 3Aand 3B, in which structure the auxiliary capacitance CS1 is formed withthe scanning line (gate line) WLn in the succeeding stage, for example,and the potential as described above is applied, the N-type MOSstructure formed by the scanning line, the gate insulating film, and theN-type semiconductor film cannot provide a sufficient capacitance.

FIG. 4 is a graph showing capacitance-voltage characteristics of theN-type MOS structure.

When −2 V, for example, is applied to the scanning lines WLn−1 and WLnshown in FIG. 3B and thereby Tr1 is maintained in an OFF state, sinceCS1 is charged while Tr1 is in an ON state, the semiconductor electrodeof CS1 is at a higher potential than the scanning lines WLn−1 and WLn,and the gate voltage applied to CS1 is a negative voltage. This causesmajority carrier electrons to be repelled from a surface of thesemiconductor film and a depletion layer (and/or an inversion layer) tobe formed on the surface of the semiconductor film, which corresponds toan increase in thickness of the insulating layer of CS1. Thus, aresulting capacitance is small.

This tendency is shown in FIG. 4. When the scanning potential is used ina range of about 1.5 V and lower, only a small capacitance is providedby the N-type MOS capacitance at all times.

In order to increase the capacitance of the auxiliary capacitance CS1,phosphorus (for making an N+ type) or boron (for making a P+ type) needsto be injected at a high concentration into the semiconductor filmelectrode of the auxiliary capacitance CS1. This causes problems of anincrease in the number of processes, a decrease in yield resulting fromoccurrence of defects, and the like.

FIGS. 5A to 7B illustrate an example of a process of manufacturing theconventional liquid crystal display device.

In FIG. 5A, gate electrodes (scanning lines) 102 a and 102 b serving asscanning lines are formed on a glass substrate 101. A metal such as Ta,Cr, Mo, Ti, Al or the like is used for the material of the gateelectrodes, and the pattern is formed by wet etching or dry etchingfollowing a photoresist process.

In FIG. 5B, an gate insulating film 103 and a semiconductor layer 104 aare formed over the gate electrodes 102 a and 102 b. Examples of thegate insulating film 103 include silicon nitride film and silicon oxidefilm, as well as anodized film obtained by anodizing a gate electrodeand the like. As the semiconductor film, amorphous silicon film,polysilicon film obtained by crystallizing amorphous silicon film,polysilicon film formed directly, or the like is used.

In FIG. 5C, a protective insulating film 105 is formed on thesemiconductor film 104 a. As the protective insulating film 105, siliconnitride film, silicon oxide film or the like is used.

In FIG. 5D, resists 107 a and 107 b are formed in a self-aligning mannerwith the gate electrodes 102 a and 102 b serving as a light shield mask.The protective insulating film 105 is thereafter removed by wet etchingor dry etching. Then, using remaining protective insulating films 105 aand 105 b as a mask, the semiconductor film is doped with phosphorus (P)or the like at a low concentration. A doped portion of the semiconductorfilm is denoted as 104 b. The semiconductor film 104 b is an n⁻ typesemiconductor.

In FIG. 6A, a resist 108 having such a shape as to cover a portionforming an LDD region in the pixel transistor is formed. In order toremove the protective insulating film 105 b remaining in a portion wherethe auxiliary capacitance is formed, wet etching or dry etching isthereafter performed.

Then, phosphorus or the like is injected at a high concentration tothereby metalize the semiconductor layer 104 b. A metalized portion ofthe semiconductor film 104 b is denoted as 104 c.

Though not shown in the figures, a photoresist process and an injectionprocess are carried out according to a portion for injection of a secondtype of dope (boron or the like). Thereafter heat treatment is performedas required to activate doped elements.

The wet etching or the dry etching is usually performed by a processwith etching selectivity to protect the semiconductor layer 104 b fromthe etching. However, when there is a pin hole or the like in thesemiconductor layer 104 b, the gate insulating film 103 serving as abase is etched. The etched portion, being greatly deteriorated in termsof withstand voltage, forms a path of current leakage, and causes adefect such as a point defect or the like. Besides, the process forremoving the protective insulating film 105 b is added, which representsa cost increasing factor.

In FIG. 6B, for device isolation, the semiconductor layer 104 c on theoutside of the gate electrodes 102 a and 102 b is removed using meanssuch as photolithography, dry etching or the like.

In FIG. 6C, an interlayer insulating film 109 is formed by siliconnitride film, silicon oxide film or the like. Thereafter contact holes110 a and 110 b are formed using means such as photolithography, wetetching or the like.

In FIG. 7A, a metal such as Al, Ta, W or the like is formed as datasignal lines 111 a and 111 b and a connecting metal 112 for connectionwith a pixel electrode. Thereafter the metal is removed using means suchas photolithography, dry etching or the like, whereby a pattern isformed.

In FIG. 7B, a second interlayer insulating film 113 is formed by siliconnitride film, silicon oxide film or the like. In order to provide thislayer with a flattening effect, a photosensitive organic film, aphotosensitive SOG (spin on glass) film or the like may be used. Also inthis process, a contact hole for connection with the pixel electrode 114is formed. Thereafter the pixel electrode 114 is formed using atransparent conductive film of ITO, IXO or the like.

Then, though not shown in the figures, a corresponding color filtersubstrate prepared separately is superposed on the TFT substrate, anassembly process is carried out with a liquid crystal layer sandwichedbetween the color filter substrate and the TFT substrate, and further apolarizer and the like are attached, whereby the liquid crystal displaydevice is completed.

Thus, with the conventional manufacturing method, a special process isrequired to complete the structure of the auxiliary capacitance, whichconstitutes a cost increasing factor, and also leakage current thatcauses defects is increased. There are conventionally problems of suchan increase in the number of processes and a decrease in yield resultingfrom occurrence of defects.

While a conventional example of the bottom gate type transistor in whichthe scanning line (gate electrode) is formed under the semiconductorlayer has been described above, there are also problems in a method ofmanufacturing the top gate type transistor in which the scanning line(gate electrode) is formed above the semiconductor layer.

FIGS. 8A, 8B, and 8C and FIGS. 9A and 9B illustrate a conventionalexample of a method of manufacturing a liquid crystal display devicehaving the structure of the top gate type transistor.

As shown in FIG. 8A, a base layer 122 and a semiconductor layer 123 aare formed on a glass substrate 121. As the base layer 122, siliconnitride film or silicon oxide film, for example, is used. As thesemiconductor layer 123 a, amorphous silicon film, polysilicon filmobtained by crystallizing amorphous silicon film, polysilicon filmformed directly, or the like is used.

As shown in FIG. 8B, in order to obtain a region for device isolation, apart of the semiconductor layer 123 a is removed using means such asphotolithography, dry etching or the like.

A gate insulating film 124 is then formed on the semiconductor film 123a. Examples of the gate insulating film include silicon nitride film,silicon oxide film and the like.

Then, gate electrodes 125 a and 125 b are formed in a region for forminga transistor TFT and a region for forming an auxiliary capacitance.

Next, the semiconductor film is doped with phosphorus or the like at alow concentration in a self-aligning manner with the gate electrodes 125a and 125 b serving as an injection mask. A doped portion of thesemiconductor film is an n⁻ type semiconductor, and is denoted as 123 b.

As shown in FIG. 8C, a resist 126 having such a shape as to cover aportion forming an LDD region in the pixel transistor TFT is formed.Phosphorus or the like is injected into other regions at a highconcentration to thereby metalize the semiconductor layer 123 b. Themetalized portion of the semiconductor film 123 b is denoted as 123 c.

Though not shown in the figures, a photoresist process and an injectionprocess are carried out according to a portion for injection of a secondtype of dope (boron or the like). Thereafter heat treatment is performedas required to activate doped elements.

In FIG. 9A, an interlayer insulating film 127 is formed by siliconnitride film, silicon oxide film or the like. Thereafter contact holes128 a and 128 b are formed using means such as photolithography, wetetching or the like.

In FIG. 9B, a metal such as Al, Ta, W or the like is formed as datasignal lines 129 a and 129 b and a connecting metal 130 for connectionwith a pixel electrode 132. Thereafter the metal is removed using meanssuch as photolithography, dry etching or the like, whereby a pattern isformed.

Then, a second interlayer insulating film 131 is formed by siliconnitride film, silicon oxide film or the like. In order to provide thislayer with a flattening effect, a photosensitive organic film, aphotosensitive SOG (spin on glass) film or the like may be used. Also inthis process, a contact hole for connection with the pixel electrode 132is formed. Thereafter the pixel electrode 132 is formed using atransparent conductive film of ITO, IXO or the like.

Then, though not shown in the figures, a corresponding color filtersubstrate prepared separately is superposed on the TFT substrate, anassembly process is carried out with a liquid crystal layer sandwichedbetween the color filter substrate and the TFT substrate, and further apolarizer and the like are attached, whereby the liquid crystal displaydevice is completed.

As shown in FIGS. 8B and 8C, the above structure has the gate electrode125 b formed in a region for forming the auxiliary capacitance.Therefore no impurity can be injected into the semiconductor film 123 aunder the gate electrode 125 b, and the semiconductor film 123 a underthe gate electrode 125 b cannot be metalized. In order to solve thisproblem within the scope of the conventional method, it is necessary toadd processes of forming a mask, performing injection, and then removingthe mask in an initial stage, or form an independent auxiliarycapacitance line as shown in FIG. 1.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above problems, andit is an object of the present invention to provide a display devicewith a high aperture ratio and a large auxiliary capacitance and amethod of manufacturing the display device without increasingmanufacturing processes.

According to an aspect of the present invention, there is provided adisplay device including: a display element; a first scanning line; asecond scanning line; a data signal line; a switching element having afirst terminal and a second terminal of a first conduction type, thefirst terminal being connected to the data signal line, for being heldin a conducting state or a non-conducting state according to a voltageapplied to the first scanning line; and a storage capacitance having afirst electrode and a second electrode that shares the second scanningline; wherein the second terminal of the switching element is connectedto the display element and connected to the first electrode of thestorage capacitance including a semiconductor film of a secondconduction type different from the second terminal.

While the switching element is held in the conducting state, the storagecapacitance is charged from the data signal line via the switchingelement, and while the switching element is held in the non-conductingstate, the storage capacitance applies a voltage to the display element.

The second terminal of the switching element and the first electrode ofthe storage capacitance are connected to each other by a conductivematerial.

Specifically, the second terminal of the switching element and the firstelectrode of the storage capacitance are connected to each other by aconductive material deposited in a contact hole reaching the secondterminal of the switching element and a contact hole reaching the firstelectrode of the storage capacitance.

Alternatively, the second terminal of the switching element and thefirst electrode of the storage capacitance are connected to each otherby a conductive material deposited in a contact hole reaching the secondterminal of the switching element and the first electrode of the storagecapacitance.

Preferably, the conductive material for connecting the second terminalof the switching element and the first electrode of the storagecapacitance to each other is identical with a conductive material usedfor the data signal line.

Further, preferably, a part or a whole of the storage capacitance isformed between the data signal line and the second scanning line in aregion where the data signal line and the second scanning line overlapeach other.

According to a second aspect of the present invention, there is provideda display device including: a plurality of first scanning lines andsecond scanning lines; a plurality of data signal lines; a plurality ofpixels arranged in a form of a matrix; and a driving circuit for drivingthe plurality of pixels; wherein the driving circuit for driving each ofthe pixels includes: a switching element having a first terminal and asecond terminal of a first conduction type, the first terminal beingconnected to the data signal line, for being held in a conducting stateor a non-conducting state according to a voltage applied to the firstscanning line; and a storage capacitance having a first electrode and asecond electrode that shares the second scanning line; and the secondterminal of the switching element is connected to a display element andconnected to the first electrode of the storage capacitance including asemiconductor film of a second conduction type different from the secondterminal.

Preferably, the switching element is a thin film transistor havingpolycrystalline silicon as a semiconductor layer.

According to a third aspect of the present invention, there is provideda method of manufacturing a display device, the method including thesteps of: forming a conductive first scanning line and a conductivesecond scanning line arranged in parallel with each other, a firstinsulating film covering the first scanning line and the second scanningline, and a semiconductor film covering the first insulating film;forming a first protective mask and a second protective mask forprotecting a first channel region and a second channel region,respectively, of the semiconductor film, the first channel region andthe second channel region being opposed to the first scanning line andthe second scanning line, respectively; and injecting an impurity of afirst conduction type and an impurity of a second conduction type into aswitching element region for forming a switching element including thefirst scanning line and a storage capacitance region for forming astorage capacitance including the second scanning line, respectively, inthe semiconductor film, in a state in which the first protective maskand the second protective mask are formed.

According to the present invention, there may be provided a method ofmanufacturing a display device, the method including the steps of:forming a second insulating film so as to cover the semiconductor filmhaving the switching element region and the storage capacitance regioninjected with the impurity of the first conduction type and the impurityof the second conduction type, respectively, and the first protectivemask and the second protective mask; forming, in the second insulatingfilm, a first contact hole and a third contact hole reachingsemiconductor regions of the first conduction type on both sides of thefirst scanning line; forming, in the second insulating film, a secondcontact hole reaching a semiconductor region of the second conductiontype on one side of the second scanning line; connecting thesemiconductor region of the first conduction type on one side of thefirst scanning line with the semiconductor region of the secondconduction type on one side of the second scanning line by depositing aconductive material in the first contact hole and the second contacthole; and forming a data signal line by depositing a conductive materialin the third contact hole.

Preferably, the first contact hole is a same contact hole as the secondcontact hole.

Further, preferably, the conductive material deposited in the firstcontact hole and the second contact hole is a same material as theconductive material deposited in the third contact hole.

Further, according to a fourth aspect of the present invention, there isprovided a method of manufacturing a display device, the methodincluding the steps of: forming a semiconductor film, an insulating filmcovering the semiconductor film, and a conductive first scanning lineand a conductive second scanning line arranged in parallel with eachother on the insulating film; and injecting, from a side of the firstscanning line and the second scanning line, an impurity of a firstconduction type and an impurity of a second conduction type into aswitching element region for forming a switching element including thefirst scanning line and a storage capacitance region for forming astorage capacitance including the second scanning line, respectively, inthe semiconductor film.

According to the present invention described above, in the semiconductorfilm, the conduction type of a source and drain region of a transistor(the conduction type of a channel between the source and drain, so tospeak) is opposite to the conduction type of a semiconductor film regionfor forming an auxiliary capacitance. When the conduction type of thesource and drain region of the transistor and the channel is an N-type,for example, the semiconductor film region for forming the auxiliarycapacitance is made to be of a P-type. Thus, by applying a scanning linevoltage (zero or negative) that turns off the N-channel transistor tothe auxiliary capacitance of a P-type MOS structure, a large capacitanceis obtained. Also, when the conduction type of the source and drainregion of the transistor and the channel is the P-type, and when thesemiconductor film region for forming the auxiliary capacitance is madeto be of the N-type, the same effects are obtained.

In addition, at the time of injection of impurities to form the abovestructure, it suffices only to inject different types of impurities, andtherefore manufacturing processes are not increased.

Further, since the above structure provides a sufficient capacitance, atthe time of injection of an impurity into the region of thesemiconductor film for forming the auxiliary capacitance, a mask forprotecting a channel forming region of the semiconductor film whichregion is opposed to the scanning line does not need to be removed byetching. Thus defect causing factors are reduced.

According to the present invention, a conventionally impossiblestructure of a switching transistor and an auxiliary capacitance is madepossible, which increases the auxiliary capacitance and improves anaperture ratio.

In manufacturing the display device according to the present invention,an effective auxiliary capacitance can be formed without an increase inthe number of processes or with a small number of processes.

In addition, since the number of times that the surface of thesemiconductor layer is exposed to wet etching and dry etching isreduced, it is possible to reduce a rate of occurrence of defects suchas a leakage current between the semiconductor layer and the gateelectrode for the auxiliary capacitance and the like, thereby improvingyield.

The present invention reduces a non-transparent region, and can therebyincrease the aperture ratio greatly. It is accordingly possible toreduce backlight brightness and thus reduce power consumption.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an equivalent circuit of an example of a conventionaldisplay device;

FIG. 2 is a plan view of a configuration of the conventional displaydevice shown in FIG. 1;

FIG. 3A shows an equivalent circuit of another example of a conventionaldisplay device having a bottom gate structure, and FIG. 3B is a planview of a configuration of the display device;

FIG. 4 is a graph showing a result of measurement of voltage-capacitancecharacteristics of an auxiliary capacitance in the conventional displaydevice shown in FIGS. 3A and 3B;

FIGS. 5A, 5B, 5C, and 5D are sectional views of assistance in explaininga method of manufacturing the conventional display device shown in FIGS.3A and 3B;

FIGS. 6A, 6B, and 6C are sectional views, continued from FIGS. 5A, 5B,5C, and 5D, showing assistance in explaining the method of manufacturingthe conventional display device shown in FIGS. 3A and 3B;

FIGS. 7A and 7B are sectional views, continuing from FIGS. 6A, 6B, and6C, showing assistance in explaining the method of manufacturing theconventional display device shown in FIGS. 3A and 3B;

FIGS. 8A, 8B, and 8C are sectional views of assistance in explaining amethod of manufacturing a conventional display device having a top gatestructure;

FIGS. 9A and 9B are sectional views, continuing from FIGS. 8A, 8B, and8C, showing assistance in explaining the method of manufacturing theconventional display device having the top gate structure;

FIG. 10A shows an equivalent circuit of a display device according to afirst embodiment of the present invention, and FIG. 10B is a plan viewof a configuration of the display device;

FIG. 11 is a sectional view of a structure of the display deviceaccording to the first embodiment of the present invention;

FIGS. 12A, 12B, and 12C are timing charts of scanning line signals andpixel potential in the display device according to the first embodimentof the present invention;

FIG. 13 is a graph showing a result of measurement ofvoltage-capacitance characteristics of an auxiliary capacitance in thedisplay device according to the first embodiment of the presentinvention;

FIGS. 14A and 14B are sectional views of assistance in explaining amethod of manufacturing the display device according to the firstembodiment of the present invention;

FIG. 15 is a diagram showing a driving circuit in the display deviceaccording to the first embodiment of the present invention;

FIG. 16 is a plan view of a configuration of a display device accordingto a second embodiment of the present invention;

FIG. 17 is a sectional view of the configuration of the display deviceaccording to the second embodiment of the present invention;

FIG. 18 is a plan view of a configuration of a display device accordingto a third embodiment of the present invention;

FIG. 19 is a sectional view of a configuration of a display deviceaccording to a fourth embodiment of the present invention; and

FIGS. 20A and 20B are sectional views of assistance in explaining amethod of manufacturing the display device according to the fourthembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of a display device and a method of manufacturingthe same according to the present invention will hereinafter bedescribed with reference to the accompanying drawings by taking a liquidcrystal display device as an example.

First Embodiment

FIGS. 10A and 10B are diagrams showing an equivalent circuit and aconfiguration of a liquid crystal display device according to a firstembodiment. The circuit arrangement diagram of FIG. 10A is similar tothat of the conventional example shown in FIG. 3A. However, in FIG. 10A,a conduction type of semiconductor film possessed by auxiliarycapacitances PCS1, PCS2, PCS4, and PCS5 is different from a conductiontype of transistors NTr1, NTr2, NTr4, and NTr5. In this example, thetransistors NTr1, NTr2, NTr4, and NTr5 are formed by an N-channel TFT,and the auxiliary MOS capacitances are formed by a P-type MOS structure.That is, the auxiliary MOS capacitances are formed by a scanning line(metal), a gate insulating film, and a P-type semiconductor film.

The conduction types may be changed to form the transistors by aP-channel type TFT and the auxiliary capacitances by an N-type MOSstructure.

FIG. 10A shows an equivalent circuit of 2×2 pixels. A plurality ofscanning lines WLn−1, WLn, and WLn+1 in FIG. 10A are arranged inparallel with each other, and each connected to gate electrodes of thetransistors NTr1 and NTr4 or the transistors NTr2 and NTr5 formed byN-channel TFTs, for example. The scanning lines WLn−1, WLn, and WLn+1effect ON/OFF control of each of the transistors and thereby selectpixels to be operated.

The auxiliary capacitances PCS1, PCS2, PCS4, and PCS5 of the P-type MOSstructure each formed by a scanning line, a gate insulating film, and aP-type semiconductor film are each directly connected to the scanningline WLn or WLn+1.

Data signal lines BLn−1, BLn, and BLn+1 arranged in parallel with eachother for applying a voltage corresponding to a video signal to eachpixel are connected to one impurity region, for example a source regionof the transistors NTr1 and NTr2 or the transistors NTr4 and NTr5. Thedata signal lines BLn−1, BLn, and BLn+1 apply voltage to electrodes ofliquid crystal elements in pixels selected by the scanning line WLn−1,WLn, or WLn+1 while charging the auxiliary capacitances PCS of theP-type MOS structure, whereby light entering the liquid crystals ismodulated to display an image.

FIG. 10B is a plan view of the configuration of scanning lines, datasignal lines, and one pixel formed on a transparent substrate. In FIG.10B, the P-type MOS auxiliary capacitance PCS1 shown in FIG. 10A isformed on the scanning line WLn with an intermediate gate insulatingfilm not shown in the figure.

One impurity region, for example a source region of the N-channel typetransistor NTr1 is connected to the data signal line BLn−1 via aconductive material deposited in a contact hole H1. Another impurityregion, for example a drain region of the N-channel type transistor NTr1is connected to the semiconductor film of the auxiliary capacitance PCS1and an ITO electrode of an upper layer not shown in the figure viaconductive materials deposited in contact holes H2 and H3.

FIG. 11 is a schematic sectional view of the pixel structure shown inFIG. 10B. FIG. 10B is a sectional view taken along a semiconductor layerpattern from the data signal line to the auxiliary capacitance. Becauseof limited space, however, the TFT transistor portion is shown having asingle gate structure rather than a double gate structure in whichtransistors are arranged in series.

In FIG. 11, scanning lines 1 a and 1 b (WLn−1 and WLn) are formed on thetransparent substrate not shown in the figure, a gate insulating film 2is formed so as to cover the scanning lines 1 a and 1 b, andsemiconductor films 3, 4, 5, and 6 are formed on the gate insulatingfilm 2, whereby the TFT transistor and the auxiliary capacitance areformed.

In the semiconductor film, reference numeral 3 denotes an N⁺semiconductor region having a high concentration of phosphorus (P), forexample, injected therein, and reference numeral 4 denotes a P⁺semiconductor region having a high concentration of boron (B), forexample, injected therein. A center of the semiconductor film 5 is aso-called i-type semiconductor film without an impurity injectedtherein, and both sides of the semiconductor film 5 are an LDD regionhaving a low concentration of phosphorus (P), for example, injectedtherein. The semiconductor film 5 forms a channel region of the TFTtransistor. In the example of FIG. 11, this semiconductor film forms anN-channel region. Reference numeral 6 also denotes a so-called i-typesemiconductor film without an impurity injected therein.

References 7 a and 7 b denote stopper films formed so as to preventimpurity injection into the i-type semiconductor films 5 and 6 under thestopper films. Reference numeral 8 denotes an interlayer insulatinglayer.

Contact holes are formed in the interlayer insulating layer 8 on the N⁺semiconductor region 3 and the P⁺ semiconductor region 4. A conductivematerial in the contact holes forms a connecting electrode 10 forconnecting the N⁺ semiconductor region 3 and the P⁺ semiconductor region4 to each other. The conductive material also forms a data signal line9.

The gate electrode 1 a, the gate insulating film 2, and thesemiconductor films 4 and 5 form the N-channel type TFT transistor. Onthe other hand, the gate electrode 1 b, the gate insulating film 2, andthe semiconductor films 4 and 6 form a P-channel type transistor. Acapacitance of the P-channel type transistor is used as the auxiliarycapacitance.

As to conduction of the N⁺ semiconductor region 3 and the P⁺semiconductor region 4, when the N⁺ semiconductor region 3 and the P⁺semiconductor region 4 are directly connected to each other, a PNjunction occurs between the N⁺ semiconductor region 3 and the P⁺semiconductor region 4, thus causing a potential loss. It is accordinglydesirable to make a connection from the N⁺ semiconductor region 3 to theP⁺ semiconductor region 4 via a metal. In the first embodiment, themetal is deposited in the contact hole for connection to the N⁺ typesemiconductor 3 and the contact hole for connection to the P⁺ typesemiconductor 4, whereby the connecting electrode 10 is formed toconnect the N⁺ semiconductor region 3 and the P⁺ semiconductor region 4to each other.

It is desirable that a material for the connecting electrode 10 be amaterial used for the data signal line 9. The use of the same metal asthat of the data signal line 9 eliminates the need for a special processfor the connection, and thus enables manufacturing at a lower cost.

As another metal for the connection, a pixel electrode (FIG. 7B and FIG.9B) may be used.

However, the contact holes are not necessarily required; a metalliclayer may be formed directly on the N⁺ type semiconductor 3 and the P⁺type semiconductor 4.

FIGS. 12A, 12B, and 12C are timing charts of scanning line voltageapplied to the scanning lines WLn−1, WLn, and WLn+1 in the liquidcrystal display device according to the first embodiment as shown byFIG. 10A. Vdd and Vssg in FIG. 12A denote voltages for bringing the TFTtransistor of each pixel into an ON state and an OFF state,respectively. As an example, Vdd=13 V and Vssg=−2 V.

In FIG. 12B, a broken line indicates a potential of a common electrode,and an irregular line indicates timing of change in a pixel potential.

As shown in FIGS. 12A, 12B, and 12C, in displaying an image, thescanning lines WLn−1, WLn, WLn+1, . . . sequentially output a high-levelvoltage signal (Vdd) to the transistors NTr1, NTr4, NTr2, NTr5 of thepixels, and thereby turn on the transistors to operate the pixels.

For display of one screen, each pixel is operated only once. Therefore aperiod when the scanning line voltage is Vdd is far shorter than aperiod when the scanning line voltage is Vssg, and each transistor ismaintained in an OFF state during most of a period of display of onescreen. That is, the voltage of −2 V is applied to the scanning linesWLn−1, WLn, and WLn+1 during most of the display period.

Thus, the voltage of −2 V is applied to the metallic electrode (scanningline) of the P-type MOS auxiliary capacitance PCS1, for example, shownin FIGS. 10A and 10B and FIG. 11 during most of the period.

As for another electrode including the P-type semiconductor film of theauxiliary capacitance PCS1, on the other hand, when the transistor NTr1is in an ON state, a high-level signal from the data signal line BLn−1applies a voltage to electrodes on both sides of the liquid crystalwhile charging the auxiliary capacitance PCS1 via the source and drainof the transistor NTr1. Since the auxiliary capacitance PCS1 is charged,a potential of the semiconductor film electrode of the auxiliarycapacitance PCS1 is higher than Vssg. When the transistor NTr1 is in anOFF state, the source and drain of the transistor NTr1 are disconnectedfrom each other, and therefore a signal from the data signal line BLn−1does not supply a voltage to the liquid crystal and the auxiliarycapacitance PCS1. The auxiliary capacitance PCS1 supplies a voltage tothe electrodes on both sides of the liquid crystal.

As shown in the graph of the pixel potential of FIG. 12B, while thepotential of the semiconductor film of the auxiliary capacitance PCS1(the same as the pixel potential) is gradually lowered and raised, thepotential is higher than Vssg at all times. Then, a voltage Vg from themetal side (scanning line side) to the semiconductor film of theauxiliary capacitance PCS1 is negative at all times.

As already described with reference to the graph of FIG. 4, when such avoltage Vg is applied to an N-type MOS capacitance comprising a scanningline (metal), a gate insulating film, and an N-type semiconductor film,since majority carriers of the N-type semiconductor are electrons, thenegative scanning line voltage (or the voltage Vg) causes the majoritycarriers to be repelled from a surface of the semiconductor film and adepletion layer (and/or an inversion layer) to be formed, whichcorresponds to an increase in thickness of the insulating layer of theauxiliary capacitance. Thus, as shown in FIG. 4, a resulting capacitanceis small.

FIG. 13 is a graph showing capacitance-voltage characteristics of aP-type MOS structure.

In the P-type MOS capacitance comprising a scanning line (metal), a gateinsulating film, and a P-type semiconductor film, since majoritycarriers of the P-type semiconductor are holes, the negative scanningline voltage (or the voltage Vg) does not cause a depletion layer to beformed but instead causes the majority carriers to be gathered on asurface of the P-type semiconductor film. Thereby, as shown in FIG. 13,a large capacitance is obtained.

Thus, with the first embodiment, a sufficient capacitance is formed in ause range (the period when the scanning line voltage is Vssg) in normaldriving conditions.

Thus, in general, when an N-channel type pixel transistor is formed, theauxiliary capacitance needs to be formed by a P-type MOS capacitance.When a P-channel type pixel transistor is formed, it is desirable thatthe auxiliary capacitance be formed by an N-type MOS capacitance.

While in the first embodiment, the auxiliary capacitance is formed withthe scanning line (gate line) WLn in the next stage, the auxiliarycapacitance may be formed with a scanning line (gate line) WLn−2 in apreceding stage.

Conventionally, when the scanning line WLn forming the auxiliarycapacitance is raised to a high level, the pixel potential issubstantially shifted. With the P-type MOS capacitance as in the firstembodiment, when the scanning line WLn is raised to a high level, theP-type MOS capacitance is effectively decreased, and an amount of shiftis decreased, as shown in FIG. 12B. Thereby display quality is improved.

FIGS. 14A and 14B illustrate a method of manufacturing the liquidcrystal display device according to the first embodiment. Themanufacturing method according to the first embodiment is obtained bychanging the conventional process shown in FIG. 6A in the conventionalmanufacturing method shown in FIGS. 5A to 5D, FIGS. 6A to 6C, and FIGS.7A and 7B.

Following the process of FIG. 5D, in FIG. 14A, phosphorus is injected ata high concentration in the vicinity of the TFT transistor to therebyform the N⁺ semiconductor region 3 and thus metalize the semiconductorlayer. At this time, a resist 11 b is formed so as to prevent thehigh-concentration injection of phosphorus in the vicinity of theauxiliary capacitance. Thus, as in the process of FIG. 5D, an N⁻ typesemiconductor region 4 a is formed around the auxiliary capacitanceafter the high-concentration injection of phosphorus.

In addition, the conventional process of removing the protectiveinsulating film on the auxiliary capacitance is not required.

In FIG. 14B, the resist pattern 11 b in the vicinity of the auxiliarycapacitance is removed, and boron is injected at a high concentrationaround the auxiliary capacitance to thereby form a P⁺ type semiconductorregion 4 b. At this time, a resist 11 c is formed so as to prevent thehigh-concentration injection of boron in the vicinity of the TFTtransistor.

Thereafter heat treatment is performed as required to activate dopedelements.

As described above, the liquid crystal display device according to thefirst embodiment includes an element of a first conduction type and aMOS structure of a second conduction type. The use of such elements ofthe two conduction types allows a CMOS type driving circuit or logicalcircuit to be formed in a display pixel region, a region outside of thedisplay pixel region, or both the regions.

FIG. 15 shows an example of configuration of a display device in whicheach pixel is driven by such CMOS. In FIG. 15, a plurality of scanninglines arranged in parallel with each other and a plurality of datasignal lines arranged in parallel with each other are driven by ascanning line driving circuit and a data signal line driving circuit,respectively, and each of pixels arranged in a form of a matrix isdriven by a driving circuit formed by an N-channel TFT and a P-type MOScapacitance, for example.

A liquid crystal display device having such a circuit can be formed by amethod as in the first embodiment without addition of a special process,and is therefore a most suitable configuration example. For example, itis desirable to use the first embodiment in a polysilicon transistorliquid crystal display device using a polysilicon film with a highmobility as a semiconductor, or the like.

According to the first embodiment, a sufficient auxiliary capacitance isobtained in a use range (the period when the scanning line voltage isVssg) in normal driving conditions. In addition, since the auxiliarycapacitance can be formed by the CS-on-gate structure, a high apertureratio is obtained.

Further, with the method of manufacturing the liquid crystal deviceaccording to the first embodiment, processes in which the semiconductorlayer is exposed to etching are reduced, and thereby defects and thelike are decreased.

Second Embodiment

In a second embodiment, another example of configuration of the liquidcrystal display device according to the present invention will be shown.

FIG. 16 and FIG. 17 are a plan view and a schematic sectional view ofthe configuration of the liquid crystal display device according to thesecond embodiment.

The liquid crystal display device shown in FIG. 16 and FIG. 17 arebasically of the same configuration as shown in FIG. 10B and FIG. 11.Therefore repeated description in the second embodiment will be omittedwhere appropriate, and in FIG. 16 and FIG. 17, the same references areused for the same components as in FIG. 10B and FIG. 11.

There is a difference between FIG. 16 and FIG. 10B, and between FIG. 17and FIG. 11 in that the contact holes H2 and H3 shown in FIG. 10B forconnecting the N⁺ type semiconductor 3 and the P⁺ type semiconductor 4to each other are combined into one contact hole H4 in FIG. 16. Theconnecting electrode 10 shown in FIG. 11 formed by depositing aconductive material in the two contact holes is converted into aconnecting electrode 30 in FIG. 17 formed by a conductive materialdeposited in the same contact hole.

It is desirable that contacts for connecting the N⁺ type semiconductor 3and the P⁺ type semiconductor 4 to each other are to be the same contacthole extending over both the conduction types. By combining the contactholes into one, an area within the pixel can be utilized effectively,thus improving the aperture ratio.

Third Embodiment

In a third embodiment, another example of configuration of the liquidcrystal display device according to the present invention will be shown.

FIG. 18 is a plan view of the configuration of the liquid crystaldisplay device according to the third embodiment.

In FIG. 18, the same references are used for the same components as inFIG. 16 and FIG. 11.

There is a difference between FIG. 18 and FIG. 11 and FIG. 16 in that apart of an auxiliary capacitance PCS1 in FIG. 18 is disposed under adata signal line BLn−1.

In this case, a region required for forming the necessary auxiliarycapacitance is formed in a region where light does not pass throughoriginally, for example a metal region (data signal line in this case).Therefore a loss in transmittance becomes smaller, and thus a highaperture ratio can be secured.

Either of a bottom gate type transistor structure and a top gate typetransistor structure may be formed in this case.

When the auxiliary capacitance PCS1 is formed under the data signal lineBLn−1 in the bottom gate structure shown in FIG. 18, a protectiveinsulating film is left on the semiconductor layer, so that a couplingcapacitance between the signal line and the semiconductor film isdecreased. This improves display quality in terms of crosstalk and thelike.

In addition, since the coupling capacitance between the signal line andthe electrode under the signal line is decreased, a total signal linecapacitance is decreased, and thus rounding of signal line potential isreduced, thereby improving display quality.

Fourth Embodiment

While the bottom gate type transistor structure has been described as anexample, the present invention is also applicable to the top gate typetransistor structure.

FIG. 19 is a sectional view of an example of configuration of a liquidcrystal display device of the top gate structure according to a fourthembodiment.

In the liquid crystal display device of FIG. 19, semiconductor films 43,44, 45, and 46 are formed on a base layer not shown in the figure formedon a transparent substrate not shown in the figure, a gate insulatingfilm 42 is formed on the semiconductor films, and further scanning lines41 a and 41 b (WLn−1 and WLn) and an interlayer insulating film 48 areformed on the gate insulating film 42. Thereby a TFT transistor and anauxiliary capacitance are formed.

Reference numeral 43 denotes an N⁺ semiconductor region, and referencenumeral 44 denotes a P⁺ semiconductor region. A center of thesemiconductor film 45 is an i-type semiconductor film, and both sides ofthe semiconductor film 45 are an LDD region. The semiconductor film 45forms a channel region of the TFT transistor. In the example of FIG. 19,this semiconductor film forms an N-channel region. Reference numeral 46also denotes an i-type semiconductor film.

Reference numeral 46 also denotes a so-called i-type semiconductor filmwithout an impurity injected therein. Contact holes are formed in theinterlayer insulating layer 48 on the N⁺ semiconductor region 43 and theP⁺ semiconductor region 44. A conductive material in the contact holesforms a connecting electrode 50 for connecting the N⁺ semiconductorregion 43 and the P⁺ semiconductor region 44 to each other. Theconductive material also forms a data signal line 49.

The gate electrode 41 a, the gate insulating film 42, and thesemiconductor films 44, and 45 form the N-channel type TFT transistor.On the other hand, the gate electrode 41 b, the gate insulating film 42,and the semiconductor films 44 and 46 form a P-channel type transistor.A capacitance of the P-channel type transistor is used as the auxiliarycapacitance.

The schematic sectional view of the structure shown above corresponds tothe structure shown in FIG. 10B. The structure shown above maycorrespond to that of FIG. 16.

Also, the pixel transistor may have an N-channel or a P-channel.

FIGS. 20A and 20B illustrate a method of manufacturing the liquidcrystal display device having the top gate structure according to thefourth embodiment. The manufacturing method according to the fourthembodiment is obtained by changing the conventional process shown inFIG. 8C in the conventional manufacturing method shown in FIGS. 8A to 8Cand FIGS. 9A and 9B.

Following the process of FIG. 8B, in FIG. 20A, a resist 47 a having sucha shape as to cover the LDD region on both sides of the channel region45 is formed in the TFT transistor region. Then, phosphorus is injectedat a high concentration in the vicinity of the TFT transistor to therebyform the N⁺ type semiconductor region 43 and thus metalize thesemiconductor layer.

At this time, a resist 47 b is formed so as to prevent thehigh-concentration injection of phosphorus in the vicinity of theauxiliary capacitance. Thus, as in FIG. 8B, an N⁻ type semiconductorregion 44 a is formed around the auxiliary capacitance after thehigh-concentration injection of phosphorus.

In FIG. 20B, the resist 47 b in the vicinity of the auxiliarycapacitance is removed, and boron is injected at a high concentrationaround the auxiliary capacitance to thereby form a P⁺ type semiconductorregion 44 b. At this time, a resist 47 c is formed so as to prevent thehigh-concentration injection of boron in the vicinity of the TFTtransistor.

Thereafter heat treatment is performed as required to activate dopedelements.

The fourth embodiment has the same effects as the first and secondembodiments.

While the present invention has been described above on the basis of thepreferred embodiments, the present invention is not limited to theembodiments described above and is susceptible of various modificationswithout departing from the spirit of the present invention.

While the foregoing embodiments have been described by taking a liquidcrystal display device as an example, the present invention isapplicable to other display devices having a similar driving method.

The present invention is not limited to the details of the abovedescribed preferred embodiments. The scope of the invention is definedby the appended claims and all changes and modifications as fall withinthe equivalence of the scope of the claims are therefore to be embracedby the invention.

1. A display device comprising: a display element; a first scanningline; a second scanning line; a data signal line; a switching elementhaving a first terminal and a second terminal of a first conductiontype, said first terminal being connected to said data signal line, andbeing held in a conducting or non-conducting state according to avoltage applied to said first scanning line; and a storage capacitancehaving a first electrode and a second electrode, said second electrodecomprising a portion of said second scanning line; wherein said secondterminal of said switching element is connected to said display elementand the first electrode of said storage capacitance, said firstelectrode consisting of a semiconductor film of a second conduction typedifferent from the first conduction type and further wherein the storagecapacitor is comprised of a p-type MOS capacitance.
 2. The displaydevice as set forth in claim 1, wherein while said switching element isheld in the conducting state, said storage capacitance is charged fromsaid data signal line via said switching element; and while saidswitching element is held in the non-conducting state, said storagecapacitance applies a voltage to said display element.
 3. The displaydevice as set forth in claim 1, wherein said second terminal of saidswitching element and said first electrode of said storage capacitanceare connected to each other by a conductive material.
 4. The displaydevice as set forth in claim 3, wherein said second terminal of saidswitching element and said first electrode of said storage capacitanceare connected to each other by a conductive material deposited in afirst contact hole reaching said second terminal of said switchingelement and a second contact hole reaching said first electrode of saidstorage capacitance.
 5. The display device as set forth in claim 3,wherein said second terminal of said switching element and said firstelectrode of said storage capacitance are connected to each other by aconductive material deposited in a contact hole reaching said secondterminal of said switching element and said first electrode of saidstorage capacitance.
 6. The display device as set forth in claim 3,wherein said conductive material for connecting said second terminal ofsaid switching element and said first electrode of said storagecapacitance to each other is identical with a conductive material usedfor said data signal line.
 7. The display device as set forth in claim1, wherein at least a part of said storage capacitance is formed in aregion where there is an overlap between one of said data signal lineand said second scanning line.
 8. A display device comprising: aplurality of first scanning lines and second scanning lines; a pluralityof data signal lines; a plurality of pixels arranged a matrix; and adriving circuit for said plurality of pixels; wherein said drivingcircuit includes: a switching element having a first terminal and asecond terminal of a first conduction type, said first terminal beingconnected to said data signal line, and being held in a conducting ornon-conducting state according to a voltage applied to said firstscanning line; and a storage capacitance having a first electrode and asecond electrode, second electrode comprising said second scanning line;and the second terminal of said switching element is connected to adisplay element and connected to the first electrode of said storagecapacitance, said first electrode a semiconductor film of a secondconduction type different from the conduction type of the secondterminal and further wherein the storage capacitor is comprised of ap-type MOS capacitance.
 9. The display device as forth in claim 8,wherein said switching element is a thin film transistor havingpolycrystalline silicon as a semiconductor layer.